System and method for abatement of food cooking fumes

ABSTRACT

A method for treating cooking fumes to oxidize oxidizeable particulate and gaseous components thereof includes contacting the fumes with a catalytic material containing ceria and alumina each having a BET surface of at least about 10 m 2  /g, for example, ceria and activated alumina in a weight ratio of from about 1.5:1 and 1:1.5 and a BET surface area of from about 25 m 2  /g to 200 m 2  /g. Optionally, a catalytic metal component such as platinum or palladium may be included in the catalytic material. The foodstuffs cooking fumes are contacted with the catalyst composition (22 or 40) at a temperature of 200° C. to 600° C. to promote the oxidation of both particulate (atomized) animal and/or vegetable oils and fats and oxidizeable gas phase components of the fumes. Optionally, a separate, supplemental gas phase oxidation catalyst (42) may be used in conjunction with and downstream of the above-described catalyst (40) to provide a two-catalyst system for treating cooking fumes.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation-in-part of application Ser. No.07/973,461, filed Nov. 19, 1992, now abandoned, in the names of RobertJ. Farrauto, Kenneth E. Voss and Ronald M. Heck and entitled "ImprovedCeria-Alumina Oxidation Catalyst and Method of Use", which in turn is acontinuation-in-part of application Ser. No. 07/798,437, filed Nov. 26,1991, now abandoned, in the names of the same three inventors andentitled "Improved Diesel Exhaust Oxidation Catalyst and Method of UsingThe Same".

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a method for the oxidation of oxidizeablecomponents of a gas-borne stream, and more specifically to the treatmentof cooking fumes to reduce the pollutants content thereof.

2. Description of the Related Art

Ongoing efforts to protect the environment from polluting by-products ofcommercial activities have led to concern regarding the release ofparticulate emissions from food cooking operations. The cooking of foodgenerates large quantities of cooking fumes which include particulateemissions, such as droplets of grease and cooking oils, carbon monoxideand hydrocarbon-derived gases including reactive organic gases. If leftuntreated, these pollutants are released into the air. Conventionalapproaches to removing particulate pollutants from cooking fumes involvefiltration of the fumes by water scrubbers or various types of filters.Filtration, however, is an expensive and inefficient method forabatement of particulate emissions, particularly in applications wherethe volume of particulate emissions is high.

As an alternative to filtration, some attempts have been made tocatalytically convert the components of cooking fumes to less noxiousspecies. For example, French Patent FR 2 663 241 discloses a method fortreating air that has been contaminated by vapors released during deepfat frying of food, the method including passing the air through amechanical filter, an electrostatic filter and an oxidation catalystcomprising platinum and alumina.

U.S. Pat. No. 4,138,220 discloses a method and apparatus forcatalytically oxidizing grease, fats, oils and/or other hydrocarbons infumes emanating from sources such as a cooking grill or the like. Thedisclosed apparatus may include a honeycomb structure having aplatinum-containing catalyst material coated thereon.

U.S. Pat. No. 5,094,222 discloses a catalytic composite, and a foodcooker containing such catalytic composite, for decomposing fats andoils by oxidation. A silicon oxide or aluminum oxide anodic oxidationfilm is formed on an air-permeable metal support and an oxidationcatalyst is carried on the surface of the anodic oxidation film. Theoxidation catalyst is selected from the group consisting of an oxide ofone or more of manganese, iron, cobalt, nickel, copper, lanthanum andcerium.

SUMMARY OF THE INVENTION

Generally, in accordance with the present invention, there is provided acatalyst composition and a method for oxidizing oxidizeable componentsof a gas-borne stream, especially particulate grease, fats and oils,e.g., for treating cooking fumes to convert at least some of theoxidizeable components thereof to innocuous materials such as H₂ O andCO₂. The method comprises contacting the fumes with a catalystcomposition comprising bulk ceria and bulk alumina and, optionally, acatalytic metal component, at a temperature high enough to catalyze theoxidation of at least the particulate grease, fats and oils("particulates") components of the fumes. In some embodiments one orboth of the ceria and the alumina are stabilized against thermaldegradation and in other embodiments the catalyst composition consistsessentially of the bulk ceria and bulk alumina and, optionally, thecatalytic metal, e.g., platinum.

The desired temperature may be attained by heating one or both of thefumes and the catalyst composition.

The present invention also provides a system for purifying cookingfumes, the system containing a catalyst as aforesaid for primarilytreating particulates placed in series flow with a catalyst designed tocatalyze the oxidation of the gaseous components of the cooking fumes.

Specifically, in accordance with the present invention, there isprovided a method for treating fumes produced by cooking foodstuffs byoxidizing oxidizeable components of the fumes. The method comprisescontacting the fumes with a catalyst composition at a temperature highenough to oxidize at least some oxidizeable components of the fumes, andthe catalyst composition comprises a refractory carrier on which isdisposed a coating of a ceria-alumina catalytic material. The catalyticmaterial comprises a combination of ceria having a BET surface of atleast about 10 m² /g, preferably 25 to 200 m² /g, and alumina having aBET surface of at least about 10 m² /g, preferably 25 to 200 m² /g.Optionally, the catalytic material may also contain a catalyticallyeffective amount of a catalytic metal component dispersed thereon, e.g.,one or more Group VIII catalytic metal components such as one or moreplatinum group metal components. The ceria and alumina may each comprisefrom about 5 to 95 percent by weight of the combination, e.g., fromabout 10 to 90 percent by weight or from about 35 to 65 percent byweight.

The ceria and the alumina of the catalyst composition used in the methodof the invention may each be disposed in respective discrete layers, oneoverlying the other, or may be disposed in intimate admixture with eachother.

In one aspect of the invention, the catalytic material comprises thecatalytically effective amount of catalytic metal component, e.g.,platinum or palladium, dispersed thereon. The platinum group metalcomponent may, for example, comprise platinum in an amount of at leastabout 0.1 g/ft³ of the composition, e.g., in an amount of from about 5g/ft³ to about 80 g/ft³ of the composition or palladium in the amount offrom about 0.1 to 200 g/ft³ of the composition. Lesser amounts ofcatalytic metal may be used in some circumstances, e.g., the platinumcatalytic component in the amount of 0.1 to 5 g/ft³ or 0.1 to 15 g/ft³of the composition.

Other aspects of the present invention include heating one or both ofthe fumes to be treated and the catalyst composition so as to contactthe fumes with the catalyst composition at a temperature of from about200° C. to 600° C.

In another aspect of the present invention, the fumes compriseoxidizeable gases and the method further includes contacting the fumeswith a gas phase oxidation catalyst after contacting the fumes with theabove-described catalyst composition to oxidize at least some of theoxidizeable gases.

In accordance with yet another aspect of the present invention, there isprovided a system for purifying fumes produced by cooking foodstuffs,which system comprises a particulates phase catalyst compositionarranged in series flow relation relative to the fumes to be purifiedwith a gas phase catalyst composition. The particulates phase catalystcomposition comprises a catalyst composition as described above and thegas phase catalyst composition comprises any suitable oxidationcatalyst, e.g., a catalyst containing a Group VIII catalytic metal.

Other aspects of the invention will be apparent from the followingdescription.

As used herein and in the claims, the following terms shall have theindicated meanings.

The term "fumes" means a gaseous stream produced upon cooking foodstuffswhich may contain gaseous components and non-gaseous components such assolid particulates and/or vapors, liquid mist or droplets, and/or solidparticulates wetted by a liquid. Cooking fumes are believed to compriseat least some of the following components: animal and/or vegetable oils,carbon monoxide, hydrocarbon-derived compounds including aliphaticcompounds such as olefins, aromatic compounds, some of which aresometimes collectively referred to in the art as a reactive organic gas("ROG") component that may comprise, e.g., gaseous alcohols, aldehydes,etc. All such gases susceptible to treatment by oxidation catalysts asherein described at a temperature of 200° C. to 600° C. are collectivelyreferred to as "oxidizeable gases".

The term "BET surface area" has its usual meaning of surface area asdetermined by the Brunauer, Emmett, Teller method of N₂ adsorption.Unless otherwise specifically stated, all references herein to thesurface area of a ceria, alumina or other component refer to the BETsurface area.

The term "activated alumina" has its usual meaning of a high BET surfacearea alumina, comprising primarily one or more of γ-, θ- and δ-aluminas(gamma, theta and delta).

The term "catalytically effective amount" means that the amount ofcatalytic material present in a composition is sufficient to increasethe rate of reaction of the oxidation of pollutants in the fumes beingtreated as compared to an otherwise identical composition which lacksthe catalytic material.

The term "inlet temperature" means the temperature of the fumes, testgas or other stream being treated immediately prior to initial contactof the fumes, test gas or other stream with the catalyst composition.

The term "ceria-alumina catalytic material" means a combination of ceriaparticles and alumina particles each having a BET surface area of atleast about 10 m² /g, i.e., a combination of high surface area bulkceria and high surface area bulk alumina, sometimes referred to as"activated alumina".

The term "combination" when used with reference to the combination ofceria and alumina refractory metal oxides includes combinations attainedby mixtures or blends of the oxides as well as superimposed discretelayers of the oxides.

The term "aluminum-stabilized ceria" means ceria which has beenstabilized against thermal degradation by incorporation therein of analuminum compound. A suitable technique for doing so is disclosed inU.S. Pat. No. 4,714,694 of C. Z. Wan et al, the disclosure of which isincorporated by reference herein, in which ceria particles areimpregnated with a liquid dispersion of an aluminum compound, e.g., anaqueous solution of a soluble aluminum compound such as aluminumnitrate, aluminum chloride, aluminum oxychloride, aluminum acetate, etc.After drying and calcining the impregnated ceria in air at a temperatureof, e.g., from about 300° C. to 600° C. for a period of 1/2 to 2 hours,the aluminum compound impregnated into the ceria particles is convertedinto an effective thermal stabilizer for the ceria. The term"aluminum-stabilized" is used for economy of expression although thealuminum is probably present in the ceria as a compound, presumablyalumina, and not as elemental aluminum.

Reference herein or in the claims to a refractory inorganic oxide suchas ceria or alumina being in "bulk" form means that the oxides, e.g.,the ceria or alumina is present as discrete particles (which may be, andusually are, of very small size, e.g., 10 to 20 microns in diameter oreven smaller) as opposed to having been dispersed in solution form intoanother component. For example, the thermal stabilization of ceriaparticles (bulk ceria) with alumina as described above with respect toU.S. Pat. No. 4,714,694 results in the alumina being dispersed into theceria particles and does not provide the dispersed alumina in "bulk"form, i.e., as discrete particles of alumina.

As used herein or in the claims, "Group VIII metal" catalytic componentincludes catalytically active forms (usually the element, alloy oroxide) of one or more of iron, cobalt, nickel ruthenium, rhodium,palladium, osmium, iridium and platinum, and "platinum group metal"means and includes platinum, palladium, rhodium, iridium, osmium andruthenium.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1, 2 and 3 are plots showing weight loss on the left-sideordinates and exothermic release on the right-side ordinates withtemperature on the abscissae, for TGA/DTA analyses of catalyticmaterials used in one embodiment of the present invention with corn oil(FIG. 1), canola oil (FIG. 2) and diesel lube oil (FIG. 3),respectively;

FIG. 4 is a schematic view of a restaurant char-broiler system fittedwith a catalyst for purifying cooking fumes in accordance with oneembodiment of the present invention; and

FIG. 5 is a schematic view of a restaurant char-broiler including acatalyst system for purifying cooking fumes in accordance with anotherembodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS THEREOF

Generally, the present invention relates to a method for treatingcooking fumes to abate the pollutants therein by contacting the fumeswith a catalytic material as described herein. The catalytic materialcomprises a combination of bulk ceria and bulk alumina and mayoptionally further comprise a catalytically active platinum group metalcomponent. Cooking fumes, especially those engendered by frying,especially deep oil frying, or broiling, especially of fowl or meat,engenders both oil and grease particulates as well as gaseous pollutantssuch as hydrocarbon-derived gases, reactive organic gases and carbonmonoxide, i.e., oxidizeable gases.

One novel characteristic of the present invention is believed to residein a catalyst and method for purifying cooking fumes in which thecatalyst comprises a combination, e.g., a mixture, of bulk ceria andbulk alumina as a catalytic material, without the addition of a platinumgroup metal catalytic component thereto. It is preferred that the bulkceria and the bulk alumina will each have a surface area of at leastabout 10 m² /g, preferably at least about 20 m² /g. For example, thebulk alumina may comprise activated alumina and may have a surface areaof from about 120 to 180 m² /g and the bulk ceria may have a surfacearea of from about 70 to 150 m² /g. It has been found that, inaccordance with one aspect of the present invention, surprisingly, acombination of high surface area bulk alumina and a high surface areabulk ceria provides a catalytic material which effectively catalyzes theoxidation of certain components of cooking fumes, e.g., the particulatecomponents, so as to provide a significant reduction in total cookingfume emissions. It should be noted that the prior art generallyconsiders refractory base metal oxides such as alumina and ceria to bemerely supports for the dispersal thereon of catalytically active metalssuch as platinum group metals. In contrast, the present inventionteaches that a catalytic material consisting essentially of acombination of bulk ceria and bulk alumina of sufficiently high surfacearea (10 m² /g or higher as described above) dispersed as a thin coatingon a suitable carrier, provides an effective cooking fume oxidationcatalyst which is effective for catalyzing the oxidation of particulate(e.g., aerosol droplets) of animal and vegetable greases, oils and fats.The addition of a platinum group metal or other catalytic metal speciesthereon is optional, but provides greater efficacy in also convertingoxidizeable gaseous components of the cooking fumes to innocuoussubstances. As used herein, "innocuous substances" include H₂ O andcarbon dioxide. Thus, beneficial effects are attained by the optionalincorporation of suitable catalytic metal components, e.g., platinumand/or palladium, and/or oxides of iron, nickel and/or cobalt, in theceria-alumina catalytic materials described above.

The method of the present invention may be achieved by contactingcooking fumes with the catalyst materials of the present invention at atemperature high enough to catalyze the oxidation of at least theparticulate oil fraction of the fumes. Typically, the operatingtemperature is from about 200° C. to 600° C., preferably from about 200°C. to 400° C.

The catalytic materials of the present invention may take the form of acarrier or substrate, sometimes in the art referred to as a "honeycomb"structure and described below in more detail, on which the catalyticmaterial is dispersed as a coating.

The Catalytic Materials

The catalytic materials used in accordance with the present inventionmay be rendered in the form of an aqueous slurry of fine particles ofceria and alumina which, in some embodiments, may be impregnated with asolution or other dispersion of a platinum group metal compound.Typically, the refractory metal oxide particles are mixed with water andan acidifier such as acetic acid, nitric acid or sulfuric acid, and ballmilled to a desired particle size. The slurry is then applied to asuitable carrier, dried and calcined to form a catalytic materialcoating (sometimes called a "washcoat") thereon.

When the optional catalytic metal component is used with the combinationof ceria and alumina, the catalytic metal component may be dispersedonto the alumina particles or onto both the ceria and alumina particles.In the latter case, the ceria-alumina combination acts not only as acatalyst but also as a support for the optional platinum catalytic metalcomponent. Such incorporation of platinum group metal may be carried outafter the ceria-alumina catalytic material is coated as a washcoat ontothe carrier, dried and calcined, by impregnating the calcined coatedcarrier with e.g., a solution of a suitable platinum compound, followedby drying and calcining the impregnated ceria-alumina coating. However,preferably, the alumina particles or both the ceria and aluminaparticles are impregnated with a suitable catalytic metal or metalscompound or compounds before a coating of the ceria-alumina catalyticmaterial is applied to the carrier. In either case, the optionalcatalytic metal component may be added to the ceria-alumina catalyticmaterial as, e.g., one or more solutions of soluble metal compound(s),the solution(s) serving to impregnate the ceria and alumina particles(or the ceria-alumina coating on the carrier), which may then be driedand the catalytic metal component fixed thereon. Fixing may be carriedout by calcination or by treatment with hydrogen sulfide or by otherknown means, to render the catalytic metal component in water-insolubleform.

Generally, the slurry of admixed ceria and alumina particles, whether ornot impregnated with a catalytic metal component, will be deposited uponthe carrier substrate which is then dried and calcined to adhere thecatalytic material to the carrier and, when the catalytic metalcomponent is present, to revert the catalytic metal component to theelemental metal or its oxide. For example, in the case of a platinumcatalytic metal component, suitable platinum compounds for use in theforegoing process include potassium platinum chloride, ammonium platinumthiocyanate, amine-solubilized platinum hydroxide and chloroplatinicacid; these and other platinum compounds and compounds of other platinumgroup metals, e.g., palladium, rhodium, etc. as well as compounds ofother catalytic metals suitable for the purpose, are well-known in theart. During calcination, or at least during the initial phase of use ofthe catalyst, such compounds, if present, are converted into thecatalytically active elemental metals or oxides.

When the catalytic material is applied as a thin coating to a suitablecarrier, as described below, the proportions of ingredients areconventionally expressed as weight of material per unit volume ofcatalyst, as this measure accommodates the presence of different sizesof catalyst composition voids provided by different carrier wallthicknesses, gas flow passages, etc. Grams per cubic inch ("g/in³ ")units are used to express the quantity of relatively plentifulcomponents such as the ceria-alumina catalytic material, and grams percubic foot ("g/ft³ ") units are used to express the quantity of thesparsely used ingredients, such as the platinum metal. For typicalcooking fume applications, the ceria-alumina catalytic material of thepresent invention generally may comprise from about 0.25 to about 4.0g/in³, preferably from about 0.25 to about 3.0 g/in³ of the coatedcarrier substrate, optionally including a catalytic metal component suchas platinum in amounts of from about 0 to about 90 g/ft³, preferablyfrom about 0 to 25 g/ft³, of platinum calculated as the elemental metal.

Generally, other ingredients may be added to the catalyst composition ofthe present invention such as conventional thermal stabilizers for therefractory inorganic oxides. For example, it is known that high surfacearea alumina can be thermally stabilized with rare earth metal oxidessuch as ceria and bulk ceria can be stabilized with alumina. Thermalstabilization of high surface area ceria and alumina to militate againstphase conversion to less catalytically effective low surface area formsis well-known in the art. Such thermal stabilizers may be incorporatedinto the bulk ceria or into the bulk activated alumina, by impregnatingthe ceria (or alumina) particles with, e.g., a solution of a solublecompound of the stabilizer metal, for example, an aluminum nitratesolution in the case of stabilizing bulk ceria or a cerium nitratesolution in the case of stabilizing alumina. Such impregnation is thenfollowed by drying and calcining the impregnated particles. Thus, forexample, ceria particles impregnated with aluminum nitrate are calcinedto convert the aluminum nitrate impregnated therein into alumina.

In addition, the catalyst compositions of the invention may containother catalytic ingredients such as other base metal promoters or thelike. However, in one embodiment, the catalyst composition of thepresent invention consists essentially only of the high surface areaceria and high surface area alumina, preferably present in a weightproportion of 1.5:1 to 1:1.5, with or without thermal stabilizersimpregnated therein, and, optionally, platinum or palladium.

The Carrier (Substrate)

The carrier used in this invention should be relatively inert withrespect to the catalytic material dispersed thereon. Typically, carrierscomprise a body having a plurality of fine, parallel gas flow passagesextending therethrough, on the walls of which is applied a coating ofthe catalytic material of the invention. One class of carriers iscomprised of refractory ceramic-like materials such as cordierite,α-alumina, silicon nitride, zirconia, mullite, spodumene,alumina-silica-magnesia or zirconium silicate. Another class of carriersis comprised of suitable metals such as stainless steel, for example,321 stainless, or an Alpha-4 alloy, or aluminum or aluminum alloys. Thecarriers are preferably of the type sometimes referred to as honeycombor monolithic carriers, comprising a unitary body having a plurality offine, substantially parallel gas flow passages extending therethroughand connecting both end-faces of the carrier to provide a parallel flowpath "flow-through" type of carrier. Such monolithic carriers maycontain up to about 700 or more flow channels ("cells") per square inchof cross section, although far fewer may be used. For example, thecarrier may have from about 7 to 600, more usually from about 50 to 400,e.g., 60 to 100, cells per square inch ("cpsi").

While this discussion and the following examples relate to flow-throughtype carrier substrates, wall-flow carriers (filters) or tortuous flowpath carriers (foam, mesh, etc.) may also be used. Wall-flow carriersare generally similar in structure to flow-through carriers, with thedistinction that each channel is blocked at one end of the carrier body,with alternate channels blocked at opposite end-faces. Wall-flow carriersubstrates and the support coatings deposited thereon are necessarilyporous, as the exhaust must pass through the walls of the carrier inorder to exit the carrier structure. Foams and meshes provide a tortuousflow path of the gases flowed therethrough. Because pressure drop is asignificant consideration in treating cooking fumes, parallel flow pathflow-through channels are preferred as they generally impose a lowerpressure drop on the gases flowed therethrough than do other types ofcarriers. For this reason, relatively short flow path, large end faceand relatively coarse (50 to 100 cpsi) carriers are preferred.

The catalyst-bearing substrate, sometimes referred to herein as acatalyst member, is contacted with a gas stream containing particulateemissions from a food preparation process, i.e., cooking fumes.Generally, the temperature of the catalyst must be at least about 200°C. to obtain satisfactory results. Often, the cooking operation willprovide fumes of 200° C. or higher and supplemental heating is notrequired. However, since cooking fumes sometimes do not attain suchtemperatures, or the configuration of a particular cooking arrangementmay result in significant temperature loss by the fumes by the time theyreach the catalyst member, it may be necessary to heat the fumes and/orthe catalyst member at least intermittently during the purificationprocess. For example, a catalyst member comprising a substrate coatedwith a catalytic material according to the present invention may befitted above a conveyorized charbroiler of the kind commonly found infast food restaurants. Fumes generated from broiling of foodstuffs onthe conveyor is emitted from the broiler and is passed through thecatalyst member. The temperature of the fumes is usually over 200° C.but the catalyst member may be heated, if necessary, by any convenientmeans, for example, electrically or by a heating jacket surrounding thecatalyst member or a flue which conducts the fumes to the catalystmember. The invention may be employed in other food-preparationenvironments, e.g., for the treatment of fumes produced in theproduction of baked goods or any other cooked foods.

Alternatively, a catalyst member in accordance with the presentinvention may be placed in any suitable structure such as a hood or aflue in the exhaust of a cooking facility where it can accumulateparticulate emissions and condensate from the cooking fumes byadsorption of these materials onto the catalytic material coating of thecatalyst member. Periodically, such catalyst member may be heated totemperatures in the range of about 200° C. to 600° C., e.g., about 230°C. to 300° C., at which temperatures the adsorbed material will becatalytically oxidized.

Gas Phase Treatment

The catalyst member of the present invention, especially the embodimentsthereof which contain a catalytic metal component, are efficacious fortreating at least some of the oxidizeable gas components of cookingfumes as well as the particulate components thereof. Nonetheless, insome situations it may be desirable to supplement the catalyst member ofthe present invention with a separate catalyst to treat the gaseouspollutant components of the cooking fumes. In this type of arrangementthere is provided a system for purifying cooking fumes comprising acatalyst member in accordance with the present invention as describedabove, followed in series cooking fume-flow communication by a gas phaseoxidation catalyst, e.g., a catalytic metal-containing catalyst such as(but not necessarily) a platinum-containing version of the ceria-aluminacatalyst of the present invention. In one embodiment, the gas phaseoxidation catalyst may be intermittently or continuously heated to anactive temperature, e.g., about 400° C., to facilitate conversion toinnocuous substances of the gas phase pollutant emissions of the cookingfumes. Such optional heating of the gas phase catalyst, and/or of thefumes introduced thereto, may be carried out on a continuous basis inorder to facilitate conversion of the gas phase oxidizeable gases toinnocuous substances on an ongoing basis. Preferably, the optional gasphase oxidation catalyst comprises a catalytic metal, e.g., platinumgroup metal, component in an amount sufficient to enhance the conversionactivity of the gas phase catalyst composition for oxidizeable gaseseven at the relatively low temperatures (200° C. to 600° C.) used intreating cooking fumes.

System For Purifying Cooking Fumes

As noted above, satisfactory treatment of cooking fumes is attained byuse of the only ceria-alumina catalyst member of the present inventionwhich is efficacious for treating the particulate phase pollutants ofcooking fumes and, especially when the optional catalytic metalcomponent is employed, the gas phase pollutants, i.e., oxidizeablegases. A typical installation of only the catalyst of the presentinvention in a restaurant charbroiler environment is illustratedschematically in FIG. 4.

As illustrated schematically in FIG. 4, there is shown a conventionalcharbroiler 2 with a conveyor chain 4, on which articles of food 6, suchas hamburgers, steaks, chicken, fish or other food items, are beingbroiled by heat sources 8, 10. A fume exhaust system 12 is disposedabove the charbroiler 2 and comprises a hood 14 having a fume collectinginlet 14a. Hood 14 tapers inwardly in a direction moving upwardly awayfrom the charbroiler 2 for connection to an outlet duct 16 which isprovided with a blower fan 18 driven by a motor 20. A catalyst member 22is fitted directly on top of charbroiler 2 by a suitable support means24 so that the cooking fumes arising from charbroiler 2 are constrainedto flow through the parallel gas flow passages of catalyst member 22.Catalyst member 22 contains parallel gas flow passages which extend inthe direction of the arrows a. The walls of the passages are coated witha catalytic material in accordance with the present invention. Under theaction of blower fan 18 the fumes are drawn through the catalyst 22. Theparticulate contaminants in the fumes, i.e., atomized droplets of animaland/or vegetable grease, fats and oils, and the gas phase contaminantsof the cooking fumes, i.e., the oxidizeable gases such as carbonmonoxide and hydrocarbon-derived gases. These gases are oxidized withinthe catalyst 22 which may comprise a platinum oxidation catalystcomponent. The treated fumes are then discharged from outlet duct 16 tothe atmosphere.

Optionally, a second catalyst, specifically for oxidation of theoxidizeable gases component of the cooking fumes may be used downstream(as sensed in the direction of cooking fumes flow) of the ceria-aluminacatalyst of the present invention. This system for primarily treatingparticulate oil and grease fraction with the ceria-alumina catalyst andproviding primary or supplemental treatment of the gas fraction ofcooking fumes may comprise a ceria-alumina catalyst composition inaccordance with the present invention arranged in series-flowcommunication relative to the cooking fumes to be treated, with aseparate gas phase catalyst. Such a two-catalyst system is illustratedschematically in FIG. 5, where there is shown a conventional cookingrange 26 on which articles of food 28, such as hamburgers, steaks,chicken, fish or other food items, are being broiled or fried. A fumeexhaust system 30 is disposed above the cooking range 26 and comprises ahood 32 having a fume collecting inlet 32a. Hood 32 tapers inwardly in adirection moving upwardly away from cooking range 26 for connection toan outlet duct 34 which is provided with a blower fan 36 driven by amotor 38. A particulates phase catalyst composition 40 having parallelgas flow passages which extend in the direction of arrows a is fittedwithin hood 32 so that the cooking fumes arising from cooking range 26are constrained to flow through the fine, parallel gas flow passagesthereof, the walls of the passages being coated with a ceria-aluminacatalytic material in accordance with the present invention. Under theaction of blower fan 36 the fumes are drawn through particulates phasecatalyst composition 40 and then into a gas phase catalyst composition42. The particulate contaminants in the fumes, i.e., atomized dropletsof animal and/or vegetable grease, fats and oils, are oxidized withinparticulates phase catalyst composition 40 and the gas phasecontaminants of the cooking fumes, such as reactive organic gases,hydrocarbons and carbon monoxide, are oxidized within gas phase catalystcomposition 42, the latter comprising a suitable gas phase oxidationcatalyst, preferable one comprising a platinum oxidation catalystcomponent. The treated fumes are then discharged from outlet duct 34 tothe atmosphere.

One or both of particulates phase catalyst composition 40 and gas phasecatalyst composition 42 may be heated to attain a suitably elevatedtemperature to enhance the rate of catalytic oxidation. Thus, electricalheating means 44 are schematically illustrated as connected toparticulates phase catalyst composition 40 and a heating jacket 46 isfitted about outlet duct 34 and the section thereof containing gas phasecatalyst composition 42. Heating jacket 46 has a heated air inlet 46aand an air outlet 46b. Heated air, which may be obtained by providingcooking range 26 with a small air heater, is supplied to heating jacket46 via inlet 46a and the cooled heating air is withdrawn through outlet46b.

The schematic renditions of FIGS. 4 and 5 omit elements such as baffles,controls, etc., normally associated therewith.

A typical configuration for particulate phase catalyst composition 22 or40 would be a substrate made of 321 stainless steel foil of 2 milthickness configured to have hexagonal cross section gas flow passages("cells") extending parallel to each other in a cell density of 64 cellsper square inch, the substrate measuring 24 inches by 24 inches by 2inches deep (61 cm×61 cm×5.1 cm deep) for a volume of 0.67 cubic feet(19 liters). The gas flow passages extend through the short dimension ofthe structure, i.e., the gas flow passages are 2 inches (5.1 cm) inlength, and the walls thereof are coated with a thin, adherent layer ofthe ceria-alumina catalytic material in accordance with the presentinvention.

Example 1

Two samples of a combined ceria-alumina material are prepared byutilizing activated alumina having a nominal BET surface area of 150 m²/g and aluminum-stabilized ceria having a nominal BET surface area of164 m² /g. The aluminum-stabilized ceria is attained by impregnating theceria particles with a solution of an aluminum compound such as aluminumnitrate followed by calcining, to provide an aluminum content in theceria of 1.35 weight percent aluminum, based on the total weight ofceria with the weight of aluminum calculated as the metal. Presumably,the aluminum is present as alumina. Aluminum-stabilized ceria is moreresistant to thermal degradation than is unstabilized ceria. As is alsowell-known, alumina may also be thermally stabilized, usually by asimilar impregnation of the alumina with precursors of rare earth metaloxides such as ceria. However, thermal stablization of the alumina isusually not necessary at the temperatures typically encountered intreating cooking fumes, i.e., from about 200° C. to about 600° C. Thehigh surface area ceria particles and the high surface area aluminaparticles are placed in separate ball mills. A quantity of anamine-solubilized platinum hydroxide solution containing 0.2894 grams ofplatinum, a quantity of monoethanolamine ("MEA"), 97.5 cc of glacialacetic acid, 2.0 cc of an anti-foamant sold under the trademark NOPCONXZ and about 1950 cc of deionized water are employed. About one-halfthe water and sufficient MEA to adjust the pH to at least about 7 areplaced in the ball mill containing the alumina, which is milled tothoroughly blend the ingredients. Then, one-half of the platinumsolution is added and ball milling is continued for about 5 minutes.Thereafter, glacial acetic acid and anti-foamant are added and millingis continued until a particle size of at least about 90 percent byweight of the particles having a diameter of less than about 12 micronsis attained. The same process is separately repeated with thealuminum-stabilized ceria, except that MEA is not employed, includingball milling for mixing and to attain the same particle size of theceria particles. The alumina and ceria slurries are then blendedtogether to form a slurry of alumina and ceria particles in analumina-to-ceria particle weight ratio of 7:6 (dry basis) containing aplatinum compound.

Two samples were prepared: Sample A contained alumina and ceria in aweight ratio of 54 parts by weight alumina to 46 parts by weight ceria,and 0.01% platinum by weight, and Sample B contained alumina and ceriain a weight ratio of 54 parts by weight alumina to 40 parts by weightceria and 0.04% platinum by weight. Samples A and B were prepared fromslurries of particles of ceria and alumina and were dried and calcinedto provide the samples in the form of powders. Three portions of 3 gramseach of Sample A and Sample B were mixed with, respectively, 0.3 gramsof corn oil, of canola oil and, as a comparison, with 0.3 grams ofdiesel lube oil.

Each of the six resulting samples of catalytic materials mixed with therespective oils were subjected to simultaneousthermogravimetric/differential thermal analysis ("TGA/DTA" analysis) toevaluate the ability of the catalytic materials to combust the oilsthereon. Generally speaking, TGA/DTA analysis involves heating thesample and simultaneously observing the changes in weight and in theamount of heat evolved by the sample. The total weight loss relatesdirectly to the amount of oil that leaves the catalyst material, eitherby evaporation or combustion. The amount of heat evolved indicates therelative amount of oil that is combusted. A thermocouple is used todetect the release of heat from the sample, and by monitoring andplotting the voltage produced by the thermocouple, a measure of thecatalytic activity for the oxidation of the oil can be obtained. Oneuseful measure is the area under the curve of the plotted exotherm peak,which, when scaled for the amount of catalyst and the amount of oil,gives a relative measure of the catalytic activity for the combustion ofoil.

The TGA/DTA analysis plots for Sample A are shown in the attached FIGS.1, 2 and 3 for the corn oil, canola and lube oil, respectively. Theleft-side ordinates provide a scale of the weight of the sample atvarious temperatures relative to the starting weight; the right-sideordinates show the release of heat from the sample measured inmicrovolts produced per milligram of sample. The relative DTA peak areasfor both catalyst materials are given in TABLE I below.

                  TABLE I                                                         ______________________________________                                        Catalyst Relative DTA Peak Areas                                              Material Corn Oil     Canola Oil                                                                              Lube Oil                                      ______________________________________                                        A        11338        10787     12731                                         B        12577        13552     12863                                         ______________________________________                                    

The data of FIGS. 1, 2 and 3 and of TABLE I show that the catalyticmaterials in accordance with the present invention are effective for theoxidation of common cooking oils at temperatures in the range of about200° C. to about 400° C.

Example 2

A series of catalytic materials in accordance with the present inventionwere prepared by combining alumina-stabilized ceria and activatedalumina of the type described in Example 1 but with no platinum or othercatalytic metal added. The ceria comprised about 46 percent by weight ofthe ceria-alumina combination and the alumina about 54 percent byweight. Several samples of the ceria-alumina combination were taken forimpregnation with varying quantities of platinum, which was carried outas described in Example 1.

The ceria-alumina catalytic materials were made into washcoat slurriesas in Example 1. A cylindrical cordierite carrier measuring 1 inch indiameter, 3 inches in length and having 200 cells per square inch (cpsi)of end face area was immersed in one of the washcoat slurries, dried andcalcined to yield catalyst members having washcoat and platinum loadingsas follows: 1.840 grams washcoat per cubic inch with no platinum; 1.907grams washcoat per cubic inch having 5 g Pt/ft³ ; 1.835 grams washcoatper cubic inch having 14 g Pt/ft³ ; 1.917 grams washcoat per cubic inchhaving 38 g Pt/ft³ ; and 1.970 grams washcoat per cubic inch having 78 gPt/ft³. A separate platinum-containing ceria-alumina combination wasprepared and coated onto a honeycomb monolith as described above at awashcoat loading of 1.99 g/in³ to yield 78 g/ft³ platinum, with theplatinum dispersed only on the alumina.

A comparative or baseline alumina coating slurry was formed on the sametype of cordierite as used for the above samples to provide acomparative sample containing alumina loaded at 1.85 g/in³ in withoutplatinum.

Test Procedure

Smoke was generated by dripping melted lard onto a metal cruciblesituated on a hot plate to heat the crucible to a temperature of atleast 400° C. The smoke was directed upward through a vertical stainlesssteel reaction tube containing the catalyst members. A sample portion ofthe inlet fumes (about 7.8 liters/min at standard conditions oftemperature and pressure) was diverted from the reaction tube inlet andwas analyzed. The sample was flowed through three 47 mm PallflexTX4OHI2O-WW teflon-backed glass fiber filters rated to 0.3 microns, inwhich particulate emissions (i.e., grease) were collected on the filtersand weighed. The particulate concentration was calculated at about 30ppm assuming an average molecular weight of 290, corresponding to a rateof particulate emission in the range of about 120-240 mg/hr. The sampleinlet fumes were then flowed through a Rosemount 400A F.D hydrocarbonanalyzer with which the hydrocarbon concentration was recorded in ppmreferenced to methane. The reactive organic gas ("ROG") concentrationwas about 450 ppm by volume (methane basis) and the CO concentration wasabout 281 ppm.

The remaining inlet fumes were flowed through the test reactor at a rateof about 8.5 liters/min ("l/min"), corresponding to a space velocity ofabout 13,000/hr. The reaction tube was surrounded by a Lindbergh tubefurnace to heat the catalyst member to temperatures of between 230° C.and 425° C.

The entire reactor effluent was passed through a series of three 0.3micron filters, and to a hydrocarbon analyzer, and then to a gaschromatograph to measure carbon monoxide and carbon dioxide content.Observations were recorded at several temperatures, and the results areset forth below in the TABLE II.

                  TABLE II                                                        ______________________________________                                        Catalytic Material                                                                      Pgm.sup.(2)                                                                            Inlet.sup.(3)                                                                         Avg..sup.(4)                                                                         Avg..sup.(5)                                                                        Avg..sup.(6)                          Ref..sup.(1)                                                                            Load     Temp.   Part.  ROG   CO                                    Oxides    (g/ft.sup.3)                                                                           (°C.)                                                                          Conv.  Conv. Conc.                                 ______________________________________                                        Comparative                                                                   Al.sub.2 O.sub.3                                                                        --       230° C.                                                                        71.0%  17.7% 244                                                      305     92.8%  25.9% 242                                   Ceria/Alumina                                                                 CeO.sub.2 /                                                                             --       230     77.7%  43.3% 350                                   Al.sub.2 O.sub.3   305     92.5%  69.2% 392                                   CeO.sub.2 /                                                                              5       230     84.3%  64.3% 132                                   Al.sub.2 O.sub.3   305     93.7%  96.2% 0                                                        425     97.9%  97.6% 0                                     CeO.sub.2 /                                                                             14       230     87.7%  85.4% 0                                     Al.sub.2 O.sub.3                                                              CeO.sub.2 /                                                                             38       230     83.5%  95.8% 0                                     Al.sub.2 O.sub.3   305     93.1%  97.8% 0                                                        425     98.1%  99.4% 0                                     CeO.sub.2 /                                                                             78       230     79.1%  97.1% 0                                     Al.sub.2 O.sub.3   305     91.0%  97.9% 0                                                        425     96.6%  99.6% 0                                     CeO.sub.2 /                                                                             78       230     82.3%  95.8% 0                                     Al.sub.2 O.sub.3                                                                        (only on 305     92.9%  98.1% 0                                               Al.sub.2 O.sub.3)                                                                      425     97.8%  99.6% 0                                     ______________________________________                                         .sup.(1) Refractory oxides                                                    .sup.(2) Platinum group metal loading (platinum, unless otherwise             indicated)                                                                    .sup.(3) Temperature (°C.) of the reactor fumes.                       .sup.(4) Average Particulate Conversion (the percentage of particulate        originally present in the reactor inlet fumes which were converted to         innocuous substances by the catalytic treatment.                              .sup.(5) Average reactive organic gas component (ROG) Conversion. (The        percentage of ROG originally present in the reactor inlet fumes which wer     converted to innocuous substances by the catalytic treatment.)                .sup.(6) Average CO Concentration (ppm by volume) in the reactor effluent                                                                              

The data of TABLE II show that the catalytic materials of the presentinvention are effective to reduce both the particulate and reactiveorganic gas components of cooking fumes. Variations in the platinumloadings had surprisingly little effect on average particulateconversion for the ceria-alumina refractory inorganic oxide materials.The apparently good particulate conversion attained by the aluminacomparative composition without any platinum thereon is believed to bethe result of adsorption of particulates onto the alumina withoutcatalytic oxidation, and this belief was confirmed upon visualinspection of the catalyst member at the conclusion of the experiment,which showed the alumina to be darkly discolored by grease. Eventually,it is believed that the alumina would become saturated in use andincapable of further adsorption of particulates. In contrast, theceria-alumina catalysts of the present invention were not darkened bygrease to the extent that the alumina was.

In contrast to particulate conversion rates, the conversion rate for thereactive (oxidizeable) gas component of the fumes appears to vary withplatinum loading at low temperature, i.e., 230° C. At highertemperatures, i.e., 305° C. and higher, there is relatively littledifference in ROG conversion between catalyst materials comprising 5 or6 g/ft³ platinum and 78 g/ft³ platinum.

The data also generally show that a small quantity of platinum isrequired to attain abatement of CO. In some operations, removal byoxidation of particulates is sufficient to meet required operatingstandards and catalyst compositions in accordance with the presentinvention without a platinum group metal thereon will be useful in suchcases.

Example 3 A. Catalytic Materials

Two platinum-containing ceria-alumina catalytic materials were preparedgenerally as described above in Example 1. The catalytic materials wereapplied as washcoats onto metallic substrates and measuring 24 inches×24inches×2 inches deep and having 64 hexagonal cells (each 2 inches inlength) per square inch of end face area. The substates were made from2-mil SS321 (321 stainless steel) foil and had a total volume of 0.67ft³. The finished catalyst members were designated C and D. Catalystmember C comprised 1.23 g/in³ of ceria-alumina (46 weight percent ceriaand 54 weight percent alumina) and 0.32 g/ft³ platinum. Catalyst memberD comprised 1.50 g/in³ of ceria-alumina (46 weight percent ceria and 54weight percent alumina) and 30 g/ft³ platinum. Catalyst members C and Deach further comprised an alumina undercoat disposed on the carrierbeneath the ceria-alumina coating. The alumina undercoat enhancesadhesion of the ceria-alumina combination to the carrier, and is appliedby immersing the carrier in an aqueous slurry of alumina particles,removing excess slurry, and then drying and calcining the alumina-coatedcarriers before applying the ceria-alumina combination. The aluminaundercoat of catalyst members C and D were each present in the amount of0.45 to 0.50 g/in³.

The catalyst members were tested by using them to treat cooking fumesfrom the broiling of frozen, uncooked hamburgers on a NIECO Model 960natural gas charbroiler, which is a broiler commonly used in fast-foodrestaurants. The broiler was placed below a Graylord exhaust hood ratedfor 1000 CFM total exhaust with a static pressure of one and one-halfinch water column (1.5" WC). The catalyst members were placed directlyabove the charbroiler, and the cooking fumes were passed through thecatalyst members.

Approximately 9.6 l/min. of effluent from the catalyst members waswithdrawn through a probe and passed through a series of filters andthen to a hydrocarbon analyzer. The first filter was a Whatmanmultigrade GMF 150 filter 47 mm in diameter, designed to retainparticles larger than 1 micron and to prevent an increase in pressuredrop as the filter cake builds. The second and third filters were also47 mm in diameter, and were Pallflex filters rated at 0.2 microns. Afterflowing through the filters, the gas sample was flowed to thehydrocarbon analyzer, where the hydrocarbon, i.e., ROG, content wasrecorded as ppm methane.

Each catalyst was tested twice with a series of 150 hamburgers. Inaddition, the cooking process was performed without any catalyst memberin the exhaust hood to provide reference particulate and hydrocarbonlevels. Emissions are expressed in units of milligrams per pound of meatcooked. For particulates, the total weight of particulates collected onthe filters is divided by the total precooked weight of the meat. Forhydrocarbon content, the ppm of hydrocarbon-derived gases (measured asmethane equivalent) generated during the cooking are given as totals;this is multiplied by the total average sample gas flow rate to yieldtotal liters of unburned hydrocarbon generated for the test. This valueis converted to milligrams of unburned hydrocarbon per pound of meatcooked (precooked weight basis).

In testing the catalyst members, baffles were placed between the burnersand the catalyst members to provide more uniform heat distribution. Theresults are set forth below in TABLE III.

                  TABLE III                                                       ______________________________________                                                      Part..sup.(1)                                                                          Part..sup.(2)                                                                       Total.sup.(3)                                                                       UHC.sup.(4)                                Catalyst      Content  Reduc-                                                                              UHC   Reduc-                                     Member Trial  mg/lb    tion %                                                                              mg/lb tion %                                     ______________________________________                                        (NONE) 1 st   2.68     --    7.29  --                                                2 nd   2.81     --    6.88  --                                         C      1 st   0.314    88.8  0.647 90.9                                              2 nd   0.273    90.3  0.695 90.2                                       D      1 st   0.296    89.5  0.106 98.5                                              2 nd   0.213    92.4  0.073 99.0                                       ______________________________________                                         .sup.(1) Particulate Content of the Emissions                                 .sup.(2) Particulate Reduction by Catalyst Member                             .sup.(3) Total UHC (Unburned Hydrocarbons), i.e., ROG Emissions               .sup.(4) Reduction of UHC by Catalyst Members                            

The data of TABLE III show that a ceria-alumina catalytic material inaccordance with the present invention comprising a relatively smallquantity of platinum (0.32 g/in³) is highly effective for the reductionof particulate matter in cooking fumes, and that the further addition ofplatinum, even a one hundred-fold increase (30 g/in³), has little effecttoward improving the removal of particulate matter from the cookingfumes. On the other hand, significant improvement was seen with regardto the reduction of gaseous unburned hydrocarbons and ROG phase of thecooking fumes, by increasing the platinum.

While the invention has been described in detail with respect tospecific preferred embodiments thereof it will be appreciated thatvariations thereto may be made which nonetheless lie within the scope ofthe invention and the appended claims.

What is claimed is:
 1. A method for treating fumes produced by cooking foodstuffs by oxidizing at least oxidizeable particulate components of the fumes comprises contacting the fumes with a catalyst composition at a temperature high enough to oxidize at least some oxidizeable particulate components of the fumes, the catalyst composition comprising a refractory carrier on which is disposed a coating of a ceria-alumina catalytic material comprising a combination of bulk ceria having a BET surface of at least about 10 m² /g and bulk alumina having a BET surface of at least about 10 m² /g, and from 0 to about 0.5 g/ft³ of a catalytic metal component dispersed thereon.
 2. The method of claim 1 wherein the catalytic metal component is present and comprises one or more Group VIII metal components.
 3. The method of claim 2 wherein the catalytic metal component comprises one or more platinum group metal components.
 4. The method of claim 1 wherein the bulk ceria and the bulk alumina each comprises from about 5 to 95 percent by weight of the combination.
 5. The method of claim 1 wherein the bulk ceria and the bulk alumina each comprises from about 35 to 65 percent by weight of the combination.
 6. The method of any one of claims 1 through 5 wherein the bulk ceria and the bulk alumina each has a BET surface area of from about 25 m² /g to 200 m² /g.
 7. The method of claim 1 or claim 2 wherein the bulk ceria comprises aluminum-stabilized bulk ceria.
 8. The method of claim 1 or claim 2 wherein the bulk ceria and the bulk alumina are each disposed in respective discrete layers, one overlying the other.
 9. The method of claim 1 or claim 2 wherein the bulk ceria and the bulk alumina are in intimate admixture with each other.
 10. The method of claim 1 or claim 4 wherein the catalytic metal component is present and comprises a catalytically effective amount of platinum group metal component.
 11. The method of claim 10 wherein the platinum group metal component comprises platinum in an amount of at least about 0.1 g/ft³ of the composition.
 12. The method of any one of claims 1 through 5 including contacting the fumes with the catalyst composition at a temperature of from about 200° C. to 600° C.
 13. The method of claim 12 including contacting the fumes with the catalyst composition at a temperature of from about 200° C. to 400° C.
 14. The method of any one of claims 1 through 5 wherein the fumes comprise oxidizeable gases and further including contacting the fumes with a gas phase oxidation catalyst after contacting the fumes with the catalyst composition so as to oxidize at least some of the oxidizeable gases by contact with the gas phase oxidation catalyst.
 15. The method of claim 14 including continuously heating the gas phase oxidation catalyst to a temperature of from about 300° C. to 600° C. to enhance its catalytic activity.
 16. A method for treating fumes produced by cooking foodstuffs by oxidizing at least oxidizeable particulate components of the fumes comprises contacting the fumes with a catalyst composition at a temperature high enough to oxidize at least some oxidizeable particulate components of the fumes, the catalyst composition comprising a refractory carrier on which is disposed a coating of ceria-alumina catalytic material comprising a combination of bulk ceria having a BET surface of at least about 10 m² /g and bulk alumina having a BET surface of at least about 10 m² /g, and from about 5 g/ft³ to about 80 g/ft³ of a platinum catalytic metal component dispersed thereon.
 17. A method for treating fumes produced by cooking foodstuffs by oxidizing at least oxidizeable particulate components of the fumes comprises contacting the fumes with a catalyst composition at a temperature high enough to oxidize at least some oxidizeable particulate components of the fumes, the catalyst composition comprising a refractory carrier on which is disposed a coating of ceria-alumina catalytic material comprising a combination of bulk ceria having a BET surface of at least about 10 m² /g and bulk alumina having a BET surface of at least about 10 m² /g, and from about 0.1 to 200 g/ft³ of a palladium catalytic metal component dispersed thereon. 